Plastic lenses are widely used in a variety of optical products because of their easier moldability and lower cost compared to glass. For example, thermoplastic plastics such as polymethyl methacrylate and polystyrene and thermosetting plastics such as polydiethyleneglycol bisallyl carbonate are used. In recent years, UV curable resins are increasingly being used as optical materials, and such UV curable resins when used as lenses must exhibit not only the properties commonly demanded for optical materials, such as viscosity, fast-curing properties, heat resistance, low shrinkage factor and transparency, but also a high refractive index. A high refractive index for plastic lenses is necessary to achieve smaller thicknesses and lighter weights for lenses, but employing inner microlenses with high refractive indexes in CCD and CMOS image sensors can also prevent the reduced condensing, or loss of sensitivity, per pixel that occurs with increased micronization. When a plastic lens is used in the camera module of a cellular phone, the design incorporates a combination of lenses, with the first lens of the lenses used therein having a high refractive index and a high Abbe number and the second lens having a high refractive index and a low Abbe number, as an achromatic correction lens.
Many types of materials with high refractive indexes exist, but it has been extremely difficult to exhibit a high refractive index while maintaining the basic properties required for optical materials, such as high transparency and heat resistance. Patent document 1 and Patent document 2, for example, are prior art documents relating to high refraction materials used as optical materials, but both technologies provide insufficient mechanical properties.
Patent document 3 discloses a photosensitive polyorganosiloxane composition as a coating material with good storage stability, curable by ultraviolet rays, having high transparency and able to form film thicknesses of 1-150 μm. The cured product disclosed in Patent document 3 has excellent properties as an optical material, including heat resistance at 300° C. and above, and high transparency. Also, Patent document 4 discloses an inorganic/organic hybrid oligomer with excellent optical characteristics, heat resistance, transparency, insulating property and wear resistance. However, it has been difficult to simultaneously obtain a high refractive index and sufficient mechanical properties for lens materials, with only the technologies disclosed in Patent document 3 and 4. The compound with a phenyl sulfide structure disclosed in Patent document 5 maintains a high refractive index, but fails to maintain sufficient heat resistance as a lens material, and therefore yellowing deterioration occurs during the step of reflow mounting, and transparency cannot be maintained. Thus, no prior art document exists that discloses an optical material having high transparency, a high refractive index, heat resistance and crack resistance that are required for use as a permanent material such as lens.
Patent document 6, incidentally, discloses a polymerizable composition comprising a polyfunctional (meth)acrylate, but the disclosed polysilane has a different structure from the (a) polyorganosiloxane according to the invention.    [Patent document 1] Japanese Unexamined Patent Publication SHO No. 63-309509    [Patent document 2] Japanese Unexamined Patent Publication HEI No. 04-045401    [Patent document 3] European Patent Publication No. 1196478    [Patent document 4] Japanese Unexamined Patent Publication No. 2005-298800    [Patent document 5] Japanese Unexamined Patent Publication No. 2004-35857    [Patent document 6] International Patent Publication WO2005/033061